Particle Flow Simulation Study Of Compressive Mechanical Behaviors And Breakage Characteristics Of Fractured Rock Samples

Based on the needs of engineering practice,it is of great practical significance to study the deformation and failure mechanism of samples with fractures under compression.However,it’s very complicated to interpret the test results because of the non-repeatability of natural fractures when using natural rock mass materials with fractures to carry out tests.In this paper,the two-dimensional particle flow code(PFC^2D)is used to calibrate the mesoscopic parameters of the parallel-bond contact model of sandstone and simulate the mechanical behaviors and crack evolution of sandstone samples with single prefabricated fracture,double prefabricated fractures,triple prefabricated fractures,ordered and disordered multiple prefabricated fractures under the uniaxial compression.The main research contents and conclusions are as follows:Firstly,the influence laws and the sensitivity of the mesoscopic parameters（effective modulus E^*,tensile strength （?） and cohesion （?））of the parallel-bond contact model on the macro parameters（peak strengthσ_p,the modulus of elasticity E and Poisson’s ratio ν）are analyzed.It’s found that the most significant mesoscopic parameters affectingσ_p are（?） and （?）.E is significantly affected by E^*and（?）.The effective modulus E^*,（?）and（?）have significant effects onν.And the"trial and error"method is used to obtain a set of mesoscopic parameters of the parallel-bond model that can accurately reflect the macroscopic mechanical properties of the intact sandstone under uniaxial compression.Next,the mechanical behaviors and the crack evolution processes of sandstone samples with single prefabricated fracture,double prefabricated fractures and triple prefabricated fractures under uniaxial compression are simulated.When a single fracture is prefabricated,σ_ci（the initiation stress）andσ_p of the samples all increase with the increase of the fracture inclination anglesγ;the evolution of cracks is divided into three stages:the slow growth of wing cracks,the initiation of secondary cracks,and the rapid development of secondary cracks that cause the specimen to fail.When prefabricating double fractures,with the increase of fracture inclination anglesβ,σ_ciincreases firstly and then decreases,andσ_p changes irregularly;crack evolution includes four stages:initiation of cracks,slow development of cracks,rapid development of cracks and failure of samples..When the triple fractures are prefabricated,with the increase of fracture inclination anglesγ,the strength indexes decrease firstly,then increase,and finally decrease;whenγ≤15°,the samples are tensile-shear failure;when15°<γ≤60°,the failure mode of the samples are featureless;whenγ>60°,the samples are tensile failure.When prefabricating double fractures and triple fractures,the crack evolution processes of the samples can be summarized as four processes:initiation of cracks,slow development of cracks,rapid development of cracks and failure of samples.Finally,the mechanical behaviors and the crack evolution of sandstone samples with ordered and disordered multiple fractures under uniaxial compression are simulated.When the fractures are in order,the sensitivity ofσ_pto the number of fractures n is much smaller than the inclination anglesηof the fractures,and E decreases with the increase of n and increases with the increase ofη;the failure modes of the samples are affected by n andη,and are determined by inter-row and intra-row cracks of fractures.When the cracks are disordered,theσ_pand E decrease as the number m of fractures and the total length L₀of the fractures increase as a whole;and the evolution of cracks is mainly divided into three stages:initiation of cracks,stable development of cracks and failure of rock samples caused by penetration of fractures;the damage strength theory based on the Mori-Tanaka method can well verify the peak strength results of the samples with different fracture surface densities under uniaxial compression based on the simulation..